4-8-8-4 "Big Boy" Locomotives in the USA

The 4-8-8-4 wheel arrangment was unique to both the United States and to the Union Pacific Railroad. No other railroad and no other country made locomotives anything like these.

Many consider the 4-8-8-4s or "Big Boys" to be the largest steam locomotives ever built in the entire world. It would be hard to argue differently.

When the Union Pacific created plans to have a locomotive designed that could haul 3,600 ton trains unassisted over the Wahsatch Mountains east of Ogden, UT, they had plans to give the name "Wahsatch" to this wheel arrangement. However, during the construction of the first of these locomotives, an ALCO machinist wrote the words "Big Boy" on the smokebox of the locomotive. The name stuck and became the name of this locomotive type.

ALCO built 25 of these locomotives for the Union Pacific at a cost of about $265,000 each. Based on inflation, the equivalent amount of money in 2018 would be $4,700,000 per locomotive.

A Dimensional Comparison of Large Locomotives

Books and magazines will often state that the Big Boy was the largest steam locomotive ever built. But, what do they mean by "largest"? When comparing steam locomotives, many different quantities can be considered. For example, weight, length, horsepower, and tractive effort are all characteristics of how "large" a steam locomotive is. In many of these categories, a locomotive "larger" than a Big Boy can be found. Does this mean that all of those books and magazines are wrong?

If you were to ignore all of the unsuccessful and experimental locomotives, then look at the overall ratings of the remaining steam locomotives in the above categories, it would become clear that there were many large locomotives. One could argue that the Big Boys were the largest and maybe they were. But the NP Z-5, the DM&IR M-3/4, the C&O H-8, and the N&W Y6b were all examples of the largest of all successful steam locomotives.

ClassM-137Y6bR-2Z-5AC-9M-3/M-4EM-1AC-10/11/12Big Boy (4884-2)4664-5H-8 - 1600AQ2S1GL
Wheel Arrangement2-8-8-22-8-8-22-8-8-22-8-8-42-8-8-42-8-8-42-8-8-44-8-8-24-8-8-44-6-6-42-6-6-62-6-6-44-4-6-46-4-4-64-8-2+2-8-4
Cyl:Dia x Stroke26x3225x3228x3226x3224x3226x3224x3224x3223.75x3221x3222.5x3324x3019.75x2822x2622x26
Driver Diameter6358636363.5636463.568696770698448
Boiler Pressure235300240250250240235250300280260300300300200
Grate Area145106.2126182139.5125117.5139150132135.2122121.713275
Evaporative Heating Surface6,8114,9157,8697,6736,9186,7825,2986,4705,7554,6427,2406,6396,7255,6613,396
Superheater Heating Surface2,1521,4783,5153,2192,8312,7702,1182,6162,0431,7413,1862,7032,9302,085835
Weight on Drivers552,700548,500544,000558,900531,200560,257485,000531,700545,200404,200507,900432,350393,000281,440324,464
Total Engine Weight665,100611,520630,750723,400689,900695,040628,700657,900772,250634,500771,300573,000619,100608,170
Maximum Axle Weight69,08868,00070,90066,40062,10069,10067,80086,70072,00079,78040,992
Tender Weight408,250378,600372,780402,000400,700438,000382,000393,300436,500434,500428,100378,600422,000451,840
Total Engine and Tender Weight1,073,350990,1201,003,5301,125,4001,090,6001,133,0401,010,7001,051,2001,208,7501,069,0001,199,400951,6001,041,1001,060,010472,864
Overall Wheelbase108103.69106.02110.08112.99113.49112.5112.17117.58106.67112.92108.27107.62123.7683.58
Tractive Effort137,174124,644162,475145,930123,364140,093115,056123,364135,37597,352110,211125,897100,81676,40389,137
Tractive Effort Booster13,90013,40015,000
Maximum Speed50638070601004
Drawbar Horsepower5,600@256,000@4036,290@41.117,498@46 (#1608)6,300@4527,200
  1. Big Boy by William Kratville p 22
  2. La Locomotive a Vapeur by Andre Chapelon 467-470
  3. Those Amazing Cab-Forwards by George Harlan p 67
  4. Pennsy Power by Alvin Staufer p 226

Railroads that used 4-8-8-4 "Big Boy" Locomotives in the USA (data provided by Steve Llanso of Sweat House Media)

Surviving Examples of 4-8-8-4 "Big Boy" Locomotives in the USA

No.ClassF.M. WhyteGaugeRailroad LineLocationStatusBuilder InfoNotes
4014488414-8-8-44'-8½"UP UP engine house, Cheyenne, WYoperationalAlco (Schenectady) #69585, 11/1941From Pomona, CA. Reacquired by the Union Pacific in July 2013. Restored to operation on May 1, 2019. Converted to burn oil. Temporarily uses the tender of UP 3985. Became the first-ever steam locomotive to be equipped with Positive Train Control.
4004488414-8-8-44'-8½"UP US 30, Holliday Park, Cheyenne, WYdisplayAlco (Schenectady) #69575, 09/1941 Cosmetically restored in 2018.
4005488414-8-8-44'-8½"UP Forney Transportation Museum, Denver, COdisplayAlco (Schenectady) #69576, 10/1941First UP Big Boy to be converted to burn oil before UP 4014. Converted back to burn coal in March 1948. Only UP Big Boy to be involved in an accident.
4018488414-8-8-44'-8½"UP Museum of the American Railroad, Frisco, TXdisplayAlco (Schenectady) #69589, 01/1942 Displayed with UP Centennial 6913.
4017488414-8-8-44'-8½"UP National Railroad Museum, Green Bay, WIdisplayAlco (Schenectady) #69588, 01/1942 Displayed with PPR GG1 4890.
4023488424-8-8-44'-8½"UP Lauritzen Gardens, Omaha, NEdisplayAlco (Schenectady) #72780, 11/1944 Displayed with UP Centennial 6900.
4012488414-8-8-44'-8½"UP Steamtown National Historic Site, Scranton, PAdisplayAlco (Schenectady) #69583, 11/1941Underwent a cosmetic restoration between 2019 and 2021. Displayed on a curved track in front near the parking lot.
4006488414-8-8-44'-8½"UP Museum of Transportation, St. Louis, MOdisplayAlco (Schenectady) #69577, 10/1941Displayed with UP Centennial 6944. Cosmetic restoration completed in 2023.

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